This invention relates to methods and apparatus for shaping a surface on an eyeglass lens blank to cause the blank to satisfy a given prescription, a lens thereafter being cut from the blank and fitted into a frame in combination with another such lens to provide a pair of prescription eyeglasses, and deals more particularly with such a method and apparatus wherein with the aid of a data controlled machine a new, expendable and inexpensive lap, for finishing and possibly shaping a lens surface on a lens blank, is produced each time a new lens is wanted.
A common procedure in making a lens for a pair of prescription eyeglasses is to provide a lens blank, of glass or plastic, having two major lens surfaces. One of these surfaces is then cut with a cup shaped grinding wheel to give it a shape causing the blank, except for the surface quality of the cut surface, to have characteristics fairly closely approximating those of the prescribed lens. The cut surface is then further shaped through the use of a lap to cause the blank to still more closely approach the prescribed characteristics. After the worked lens surface is brought to the proper shape it is then brought to a polished condition using the same lap as used for the shaping. In some instances some of the refining of the surface quality may occur simultaneously with the shaping.
A typical machine for shaping and polishing a lens surface through the use of a lap, as described above, is shown, for example, by U.S. Pat. No. 3,893,264.
In the above described known procedure the lap surface determines the final shape of the worked surface of the lens blank. To be able to produce a lens blank satisfying any randomly given reasonable prescription it is necessary for the optical laboratory, or other lens-making facility, to have available an extremely large inventory of relatively expensive differently shaped reusable laps so that when presented with a given prescription a lap having the proper shape will be at hand for use. Even so, it is often impossible to provide a lap perfectly suiting each possible prescription and in making a lens it thus often becomes necessary to use a lap having a not quite perfect shape. Or, as a corollary to this the characteristics given in a prescription can be specified only in steps the fineness of which is determined by the extent of the lap inventory.
An eyeglass prescription at the present time commonly specifies, for each lens, values of "sphere", "cylinder" and "prism". When cylinder is specified for a given lens the worked surface of the lens blank in its finished state should be toric in shape. One reason for relying on a lap to control the end shape of the worked surface is that so-called "toric generators" commonly used to cut the worked surface, and which use cup shaped cutting wheels, fail to cut truely toric surfaces and include in the cut surface an "elliptical" error subsequently removed by the lap. That is, the lap removes a non-uniform thickness layer of material from the worked surface to bring that surface to, or at least closer to, the desired toric shape.
Furthermore, at the present time prescription eyeglass lens-making procedures and apparatus are substantially limited to producing lens surfaces the complexity of which do not exceed that of a toric surface. It is likely, however, that if a means were available to produce lens surfaces of more complex shape lenses with such surfaces might better suit the individual requirements of some eyes and might be prescribed in the future.
The above discussion applies both to single vision lenses and multifocal lenses. However, in comparison to the production of a single vision lens, the making of a multifocal lens requires the stocking of a large inventory of lens blanks having differently powered and differently configured multifocal segments so that a blank with the proper multifocal segment to fill a given prescription can be selected from the inventory. Each multifocal lens blank has a multifocal segment formed on one of its major surfaces and in producing a lens from the blank in accordance with present practice, the opposite major surface of the blank is worked to give the blank characteristics satisfying the prescription.
The general object of the invention is to provide a method and apparatus for making a prescription eyeglass lens from a lens blank, by shaping and finishing one surface of the blank, which permit a lens to be made more economically then by presently known procedures.
In keeping with the forgoing object, a more specific object of the invention is to provide a lens making apparatus and method wherein the need for a lens maker to maintain a large and costly inventory of shape defining laps is avoided, thereby reducing the capital required for setting up a lens making facility and avoiding the trouble and expense involved in selecting, removing and returning laps from and to their storage locations.
A further object of the invention is to provide a method and apparatus for making a prescription lens whereby the characteristics given by the prescription may be specified to a finer degree, and the lens be made to meet such finer specifications, than is presently generally the case.
Another object of the invention is to provide a lens making apparatus and method whereby shapes more complex then that of a toric surface, if desired, may be given to a lens surface to more closely match the resulting lens to an individual eye. Allied with this object is that of being able to cut a lens blank to include prism, if desired, in the finished lens without having to decenter or otherwise adjust the lens blank in the cutting or finishing machines as is currently usually necessary. That is, a feature of the invention is that most or all desired surface shapes, including those with prism, can be obtained with a standard uniform mounting of each lens blank in the involved machines.
Another object of the invention is to provide a lens making apparatus and method of the forgoing character wherein a single cutting tool may be used to cut lens surfaces of a wide range of curvature, thereby avoiding the necessity inherent in many present machines of having to use differently sized cutters for cutting surfaces with different degrees of curvature.
Another object of the invention is to provide an apparatus and method of the forgoing character which permit the cutting and finishing of a lens surface including a multifocal segment, thereby permitting a multifocal lens to be produced from a lens blank having initially two plain spherical or other nonsegmented surfaces.
Other objects and advantages of the invention will be apparent from the following description of preferred embodiments of the invention taken in conjunction with the accompanying drawings.